Slowly going lean while driving

[jeepme]

First of all Iam new to the site although I have come here and got great info through my entire engine install. Just finished installing a ATK street stroker engine and added the ford 24lb injectors BBK 62mm throttle body, adjustable MAP sensor and the Hesco adjustable FPR and AEM afr guage.

The issue I am having is the afr reading is good during open loop operation 14.5-14.7 once the thermostat opens afr remains the same for approximately 10 min then it slowly starts going lean while driving to the point of 17.7 to 18. I raised the fuel pressure from 40 to 43.5 which just prolonged the time that it took to start going lean by a few minutes. Adjustable map is set to 5.3 volts. All sensors have been replaced during the install and I tested them as per the FSM procedures and all tested within spec. Does this sound like possibly a fuel pump failing under load or am i missing something else.

Thanks

[jeepme]

Sorry forgot to add this is in a 1995 jeep cherokee OBD1

[Torqsplit]

Sounds like you're pretty savvy w/ the wiring. I have not attempted to adjust the MAP sensor up to this point. Get some feedback on here to ensure that's w/in range probly 1st. When i first started trying to dial in my AFR, i had issues also. I'm also challenged w/ obd1 tuning. I discovered there's a ballast resistor for the fuel pump on the drivers side inner fender, under the hood. On mine its adjacent to the brake master-cylinder. I disconnected this and soldered the wires together to bypass it. The Factory manual says its designed to reduce Fuel pump voltage during light load scenarios to lessen audible noise from the pump. I noticed a similar effect as you when trying to dial in my fuel psi. You def have to monitor it cause it'll go rich down low afterwards if you don't correct for it tho. Good luck, Hope this helps you out

[jeepme]

Ill have to look for that resister i dont recall seeing one but ill check it out.

[jeepme]

No resister on my 1995. I did find that my cps wire harness was to close to the exhaust manifold and melted which was causing a very rough running condition. Got that fixed but haven't drove it around yet to see if that might have been part of the lean condition.

[jeepme]

finally got a chance to drive it. It still had a random miss but I found the #4 injector plug loose and not making good contact. Fixed that and checked the rest of them, now it is running great and no more lean condition. Now I can finally finish breaking the engine in!!

[Cheromaniac]

Glad you found the problem. Enjoy your new beastie.